During the last two decades, touch technologies have gained acceptance in a variety of consumer applications, such as touch screens in ATMs (automated-teller machines), track pads in laptop computers, and scroll wheels in media players. The movement of an object such as a finger or stylus along a surface of the touch sensor is detected by the touch sensor to generate electrical, signals for the subsequent process.
There are many types of touch sensing methods, such as resistive sensing type, capacitive sensing type, acoustic sensing type, optical sensing type, and the like, widely used in such technique field. For a resistive touch sensor, two continuous resistive sheets are stacked together with spacers at a predetermined interval clamped between the continuous resistive sheets. In operation, the two sheets contact each other at a touch location where an object touches a corresponding place of the outside surface of the touch sensor. The centroid of the touch location is detected by reading a current change at the touch location. However, if a multiple touch happens, then such resistive touch sensor can not distinguish multiple touch locations apart.
For the capacitive sensing type, there are two sub types, i.e. a projective capacitive type and a surface capacitive type. A projective capacitive touch sensor contains a lattice electrode pattern, while a surface capacitive touch sensor includes electrodes on the edge of a continuous conductive sheet. The capacitive touch sensor determines the touch locations by detecting the change in capacitance, when a conductive object such as a metal object or a finger approaches certain positions defined as the touch locations after being touched. However, the capacitive touch sensors are insensitive to dielectric materials.
An acoustic touch sensor comprises an element for emitting sound waves and another element for receiving sound waves, which causes the sound waves to be transmitted across the surface of the touch sensor. An object touching the surface absorbs some of the energy of the sound waves, which can be detected at the touch location. An optical touch sensor works in the similar way to the acoustic touch sensor, except that light waves such as infra-red waves but not sound waves are transmitted along the surface. However; both of these two types of touch sensors require frames to install the emitting elements and the receiving element. Moreover, the contaminants, such as dust, grease, etc, can also cause false activation on, the screen and the sensibility of the touch sensor is decreased.